How to change samba mode from "standard" to "prefork"

My UCS version is 4.4.3 and Samba4 version is 4.10.1-univention,I have almost 20000 client in my cluster.Did this version support change to prefork model,If it is supported,tell me the best way to safely finish of the change,and how to set thest parameters such as"prefork children",“prefork maximum backoff”,“prefork backoff increment”.